1. Field
One embodiment of the invention relates to a disk drive in which the dynamic flying height of the head can be adjusted by supplying to the head the power calculated from the barometric pressure detected by, for example, a barometric pressure sensor.
2. Description of the Related Art
Disk drives (e.g., magnetic disk drives) having an actuator that can adjust the dynamic flying height (DFH) of the head have been hitherto known. The actuator has a slider (magnetic head slider) that holds the head (magnetic head). The actuator supports the slider and can move the slider radially over the disk (magnetic disk). As generally defined, the dynamic flying height of the head is the distance between the head and the disk (more precisely, the surface of the disk, i.e., disk surface).
Known as actuators capable of adjusting the dynamic flying height of the head are thermal actuators, piezoelectric actuators, and the like. Such an actuator can adjust the dynamic flying height of the head as its part is deformed. The thermal actuator, for example, has its slider deformed through thermal expansion. Used as a heat source (adjusting element) that achieves the thermal expansion is a heater (resistive heating element). The heater is arranged at that part of the slider which lies near the head. In the thermal actuator, the power supplied to the heater is controlled, varying the thermal expansion of the slider (head). The dynamic flying height of the head is thereby adjusted. As described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-014092, the dynamic flying height of the head is measured (or estimated) from the harmonic wave ratio of a signal reproduced by the head.
The piezoelectric actuator has a slider, a suspension and a piezoelectric element. The suspension supports the slider. The piezoelectric element is arranged on the slider (or on the suspension). A voltage is applied to the piezoelectric element, adjusting the deformation of the slider. The dynamic flying height of the head is thereby adjusted. That is, the piezoelectric actuator uses a piezoelectric element as an element (adjusting element) for adjusting the dynamic flying height of the head.
The dynamic flying height of the head changes with the barometric pressure (ambient barometric pressure) in the environment where the disk drive is used, as is described in, for example, Jpn. Pat. Appln. Publication No. 09-063220, Jpn. Pat. Appln. Publication No. 06-150522, Jpn. Pat. Appln. Publication No. 10-334626 and Jpn. Pat. Appln. Publication No. 2007-310957. More precisely, the higher the ambient barometric pressure, the higher the dynamic flying height of the head will be. Conversely, the lower the ambient barometric pressure, the lower the dynamic flying height of the head will be. In this way, if the dynamic flying height of the head changes in response to a change in the ambient barometric pressure, the head may not be able to stably write or read data with reference to a disk.
In view of this, such a technique (prior art)s disclosed in, for example, Jpn. Pat. Appln. Publication No. 09-063220 is used to maintain the dynamic flying height of the head always at a target value, not influenced by the ambient barometric pressure. In this prior art, a barometric pressure sensor measures the pressure ambient to the disk drive, and the power (i.e., voltage or current) supplied to the adjusting element of the actuator is controlled in accordance with the pressure thus measured. The dynamic flying height of the head can therefore be maintained at the target value.
With the prior art described above, however, the dynamic flying height of the head can hardly be maintained at the target value if the barometric pressure sensor fails to operate well. In particular, if the barometric pressure detected by the barometric pressure sensor is higher than the actual value, the head may be set at a dynamic flying height much smaller than the target value, as will be explained below.
If the barometric pressure detected by the barometric pressure sensor is higher than the actual value, the dynamic flying height of the head will be estimated greater than the target value. In this case, the power supplied to the adjusting element is increased over the value of the correct power that should be supplied to the adjusting element. Although the actual barometric pressure is lower than the pressure detected by the barometric pressure sensor, more power than necessary is supplied to the adjusting element. Therefore, the actual dynamic flying height of the head may be unusually set at a very low value compared to the target dynamic flying height. If the head has such a low dynamic flying height, it may contact the disk (disk medium) spinning at high speed. Consequently, the head may fail to function, or the disk (medium) may be damaged.